Explosive containing nitrocellulose coated with an alkylated diphenyl amine and preparation thereof

ABSTRACT

NITROCELLULOSE EXPLOSIVE CHARGES ARE PROVIDED WITH IMPROVED MOISTURE RESISTANCE BY TREATMENT WITH AN ALKYLATED DIPHENYL AMINE.

United States Patent 3,597,288 EXPLOSIVE CONTAINING NITROCELLULOSECOATED WITH AN ALKYLATED DIPHENYL AMINE AND PREPARATION THEREOF FredericC. Merriam, Danvers, Mass., assignor to USM Corporation, Boston, Mass.No Drawing. Filed May 15, 1969, Ser. No. 825,033 Int. Cl. C06b 19/02 US.Cl. 149-11 11 Claims ABSTRACT OF THE DISCLOSURE Nitrocellulose explosivecharges are provided with improved moisture resistance by treatment withan alkylated diphenyl amine.

The present invention relates to explosive charges and more particularlyto nitrocellulose explosive charges.

Nitrocellulose explosives are notoriously hydrophilic in nature. Underhumid conditions nitrocellulose takes on directly about two percent ofwater and this may go as high as four percent. Then, in the usualsituation where the charge is produced as a compacted mass of particlesor fibers, the same charge may blot up as much as ten to twenty percentof dry Weight, taken into capillary spaces of the charge.

On taking on moisture or Water, which as indicated they do readily, evenunder humid air conditions, the ability of nitrocellulose charges to beignited conveniently is interfered with, and ignition or'firingreliability is greatly lessened. This latter is a major concern wherethe charges are designed for use as propellants or, as sometimes re'ferred to, as low explosive charges. For ordinary commercial propellantusage, water resistance which protects firing reliability after a periodof about an hour, exposure to moisture is acceptable, but neverthelessdifiicult to obtain. For military and some commercial uses the timerequirement so far as the moisture resistance is more stringent, withperiods of 24 hours or greater moisture resistance being called for. l

Various attempts have been made to improve the moisture resistance ofnitrocellulose explosive charges. Generally these have taken the form ofcoatings, the latter intended to include deposits, impregnants, etc. aswell; most of which are waxes or polymeric in nature. And, while theyhave been successful in improving moisture resistance, these coatingshave done so with the sacrifice of ignition ability and reduction inpower output of the charges so coated. This is probably for the reasonthat the coating materials used are combustion resistant in nature underthe ignition conditions ordinarily used. As a result, and, because ofthe amounts needed to be used to contribute the desired moistureresistance, residues are left on ignition which interfere particularlywith repeated ignitions or firings, and as well cut down on power outputof the charges so coated.

Accordingly, it is an object of the present invention to producenitrocellulose explosive charges exhibiting improved moistureresistance.

Another object is to produce the indicated charges and to do so withoutsignificantly lessening ignition reliability and power output of thosecharges.

Those and other objects of the present invention are attained in anexplosive charge exhibiting improved moisture resistance comprising amass of nitrocellulose coated with an alkyl substituted diphenyl aminehaving the formula "Ice wherein R is a hydrogen or alkyl radical, R isan alkyl radical and the combination of R and R contains a total of 8 to40 carbon atoms, the amine comprising about 0.1 to 5.0 weight percentbased on the weight of nitrocellulose.

Nitrocellulose explosive charges are provided in various convenientsizes and shapes. In the case of propellant or low explosive chargesthey may be produced as caseless type pellets, pills, sheets, matricesor the like, and, as well they may be produced for cased type,cartridges, etc. Similarly, high explosive charges are provided inshapes and sizes as desired. Under any of those situations, it isnecessary to produce charges of uniform nature at least insofar asenergy output is concerned, and to do so in a safe manner. The latterhas reference to the instability and dangers attendant to handlingnitrocellulose explosives. As a result it is customary to producespecific explosive charges from nitrocellulose by a method whichmaintains the material wet during production, and accordingly in arelatively safe handling condition. In one convenient method for doingthat the nitrocellulose in particulate form, that is, as fibers, fines,particles or the like is first provided as a slurry, suspension, sol orgel in water, and, incidentally, some solubilization may also takeplace. Various additives such as dye stuffs, stabilizers, fillers,binders, ignition and burning agents, as well as other treating agentssuch as those to improve water resistance, etc. may also be included.The system so obtained, with some dewatering optional, may be thendirected into shaping or die cavities and pressed to partial dryness.Thereafter the charges so obtained are repressed and dried to final sizeand density. For convenience the present invention is described inrelation to this method and particularly by treatment carried out on thenitrocellulose while in slurry or suspension form. However, theinvention may be effected by other practices such as by treating afinished charge pellet, etc. by dipping, coating, spraying or otherapplication of the alkylated diphenyl amine.

Nitrocellulose comes in various forms depending upon its explosivecharacteristics. The present invention is particularly attractive foruse in providing water resistance to nitrocellulose of the low explosivetype or use, or that which is designed for use in propellant charges.Nitrocellulose materials having a nitrogen content of 12 to 15 percentare well adapted for this. Also, as indicated previously, nitrocellulosein particulate form, and more specifically fiber or fibrous in nature isparticularly well adapted for practice of the present invention.

In providing the nitrocellulose in suspension, about 2 to 20 weightpercent, and more preferably about 5 to 12 weight percent of theparticulate nitrocellulose may be used, together with water as thesuspending medium. The resulting suspension may be also described as aslurry, and it may take the form of a so] or gel, or combination ofboth. In providing the suspension it is pre ferred that ambienttemperatures be used. With increase in temperature, and at boiling, aslurry or suspension of smoother consistency may be obtained. However,in doing so the nitrocellulose becomes strongly acid. It is preferred tomaintain the nitrocellulose at a pH of 5-8. When the nitrocellulose ismore strongly on the acid side, difiiculty is met in acquiring goodcoating effect, while if it goes on the more strongly alkaline sidedecomposition of the nitrocellulose takes place.

In addition to nitrocellulose, the suspension may contain a number oradditives, including dyestuifs, fillers such as carbon black;stabilizers such as diethyl diphenyl urea, hydroquinone monobenzylether; binders such as polyvinyl alcohol; as well as ignition andburning agents such as tricresyl phosphate, and others. It is preferredthat the additives be kept below about 2.0 weight percent. Otherwise,they may interfere in an adverse manner, with the ignition reliabilityand power output of the explosive charges produced eventually from thesubject nitrocellulose.

Moisture resistance of the nitrocellulose is obtained by coating with aspecific class of alkyl substituted diphenyl amines. Those may berepresented by the formula where R is either a hydrogen or an alkylradical, R is an alkyl radical and the total number of carbons containedin the radicals R and R total 8 to 40 with the preferred total numberranging 10 to carbon atoms for those substituents. Monoalkylateddiphenyl amines which may be used include monooctyl diphenyl amine;monononyl diphenyl amine; monodecyl diphenyl amine; monohendecyldiphenyl amine; monododecyl diphenyl amine; monotridecyl diphenyl amine;monopentadecyl diphenyl amine; monohexadecyl diphenyl amine;monooctadecyl diphenyl amine; monononadecyl diphenyl amine; etc.Dialkylated diphenyl amines which may be used include dibutyl diphenylamine; diamyl diphenyl amine; dihexyl diphenyl amine; diheptyl diphenylamine; dioctyl diphenyl amine; dinonyl diphenyl amine; didecyl diphenylamine; dihendecyl diphenyl amine; dodecyl pentyl diphenyl amine;di(2-ethylhexyl)diphenyl amine; etc.

The preferred alkyl substituted diphenyl amines are dioctyl diphenylamine; di(2-ethyl hexyl) diphenyl amine; dinonyl diphenyl amine;didodecyl diphenyl amine; etc. Water resistance so far as the period oftime the nitrocellulose may be exposed to moisture increases withincrease in the number of carbon atoms contained in the alkylsubstituents. At the same time, however, energy output may be affected,and the desired effect required based on anticipated end use,environment of use, etc. must be taken into account in choosing theparticular alkylated diphenyl amine, or mixture of same to be used on agiven occasion.

The amount of alkylated diphenyl amine deposited or coated, which termor terms include impregnated as well, ranges about 0.1 to 5.0 weightpercent on the nitrocellulose. A more preferred range is about 0.5 to2.0 weight percent. Some variation may be exercised within the indicatedranges based on the choice of alkylated diphenyl amine and the amount ofwater resistance desired. The latter aspect will, of course, be governedto some extent by the conditions anticipated to be met in using thefinished charges, storage time before use, etc.

The alkylated diphenyl amine is prepared as a solution and in that formis added to the nitrocellulose suspension, where it coats thenitrocellulose particles, or other forms of the same as are found there.The solution uses an organic solvent. Solvents for use include, forexample, methanol, ethanol, propanol, as well as other alcohols, acetoneand other ketones, methyl Cellosolve, ethyl Cellosolve, etc. Solventswhich are somewhat miscible with water, and also convenient to removeafter treatment are preferred as, for example, ethanol.

The concentration of alkylated diphenyl amine in solution preferably mayrange about 3 to 10 weight percent, with some variation based on thenature of the particular amine and solvent system used.

The solution of alkylated diphenyl amine is introduced directly into thenitrocellulose suspension. It is recommended that stirring of the mix becarried out carefully to minimize if not prevent entrapment of air inthe mix. If air becomes entrapped, it attaches to the nitrocelluloseparticles, interfering with flow distribution of the amine and even withcoating by the latter. In addition it causes the nitrocelluloseparticles to float or rise to the surface of the liquid medium, Whereasotherwise on becoming coated with amine the particles drop to the bottomof the water medium and may be conveniently separated as by decanting,etc. It is recommended then that stirring be carried out, but that it bedone by keeping the stirring systems submerged, and avoiding vortexingin the mix.

When the coated nitrocellulose settles to the bottom, the upper liquidmay be decanted to obtain preliminary separation. Thereafter the coatednitrocellulose may be washed, rinsed, provided in a further convenientslurry form and may be processed to produce charges, for example,propellant pellets, using for example, the methods and means disclosedin US. 3,430,532.

The nitrocellulose charge or charges obtained, for example, in the formof pellets, but in other convenient forms as well, exhibit improvedmoisture resistance. Further improvement in moisture resistance isdesirable in instances where it is anticipated that the charges will beexposed to moisture for an extended period of time. One method ofaccomplishing this involves treating the coated nitrocellulose chargesat elevated temperature. This involves exposing the charges to atemperature above about the melting point of the alkylated diphenylamine used in coating the charge for a period sufficient to allow thecoating to melt and form into a continuous film, which sets when thecharge is allowed to cool. Taking a dioctyl diphenyl amine coatednitrocellulose charge in pellet form, for example, treatment at C. for aperiod of at least about 10 minutes is found to contribute improvedmoisture resistance.

The following example is included for the purpose of furtherillustrating the invention.

EXAMPLE I (A) Preparation of nitrocellulose suspension A washingsolution is prepared constituting 10 liters of tap water to which isadded 60 ml. of 0.1 weight percent sodium lauryl sulfate and 200 ml. of0.1 weight percent potassium citrate.

One hundred grams (7 0 grams dry weight) of refrigerated, dampnitrocellulose are mixed into 2500 ml. of the washing solution using aclosed mixer. Even mixing is carried out for 2 minutes. A milky slurryor suspension is obtained. This is then stirred into the remainder ofthe washing solution.

After standing for 1.5 to 2.0 hours most of the nitrocellulose settlesto the bottom, in fibrous form. The top layer of hazy water is pouredoff leaving the bulk of the nitrocellulose in the bottom 625-750 ml. Thelatter is rewashed by stirring in 5.0 liters of water, at roomtemperature containing 50 ml. of 0.1 weight percent potassium citrate.The fibrous nitrocellulose is allowed to settle to 500 ml. in 2-4 hours,and again the hazy top water is poured oif.

The concentrated, non-flowable, washed fiber slurry or suspension isincreased to 1250 ml. by addition with stirring, of distilled water. Theresult is a slurry or suspension containing 5.6 weight percent solids offibrous nitrocellulose.

(B) Treatment of nitrocellulose/suspension Two hundred and fifty ml. ofthe washed fibrous nitrocellulose suspension from pragraph A above ischarged into a Waring Blendor. With the motor operating at reducedspeed, 4 ml. of warm ethanol solution containing 0.17 gram of dioctyldiphenyl amine is quickly charged or poured into the stirring solution.At the same time a coloring charge of 4.0 ml. of ethanol containing 0.03grams of National Oil Brown M and 0.03 gram of National Oil Brown Y ispoured into the suspension. Stirring is continued for 15 minutes oruntil the dioctyl diphenyl amine has deposited on the nitrocellulosefibers. Stirring is done slowly and with care to prevent vortexing ofthe mix, which in turn would allow air to become entrapped in the mix.

The treated nitrocellulose suspension is vacuum filtered at 6 in. Hgusing two Whatman No. 19.0 cm. filter papers,

in a Buchner funnel. It is noted that about 220 ml. of water are removedin 15 seconds.

The cake, of coated, fibrous nitrocellulose is air dried between papertowels, in relative darkness, for 24 hours. The amount of dioctyldiphenyl amine pickup is calculated to be 1.3% on dry weight of thenitrocellulose.

The procedure is repeated, withthe exception that the dioctyl diphenylamine is substituted for by other diphenyl amine materials. The variousproducts obtained are as follows.

Table I Nitrocellulose/ designation: Treating agent B1 Dioctyl diphenylamine. B2 Monooctadecyl diphenyl amine. B3 Monononyl diphenyl amine. B4Monooctyl diphenyl amine. -B5 Diphenyl amine.

(C) Preparation of nitrocellulose charges/pellets A number of samplesfrom each of the nitrocellulose materials produced according toparagraph B above are provided in the form of propellant charge pellets.

The samples are each weighed out to .16 gram, and placed in a covereddie having a cylindrical die cavity to provide a pellet having in eachinstance a diameter of .338 inch and a length of 0.072 inch. The pelletsare pressed in the die using a laboratory press having a 1.875 inch ram,hand pump and Marsh Type 1 Master Gauge (0-3000 p.s.i.). Pressing iscarried out at 1200 p.s.i. The pellets so obtained have a density ofabout 1.52 grams/ml.

(D) Moisture resistance testing Various of the pellets producedaccording to pragraph C above are subjected to moisture resistancetesting.

Covered glass dishes are used which are 2.0 inches in diameter and 1.2inches deep. A wet paper towel is placed over the inside bottom of thedishes and the pellets are then stationed on end on the wet paper. Theatmospheres in the glass dishes are maintained saturated. After a periodof two hours the pellets are removed, excess water wiped off and theyare transferred to glass weighing bottles, and weighed for a second timeto arrive at the water pickup.

The results obtained as a result of two hours exposure to the testingconditions are as follows.

Table II Nitrocellulose Moisture pickup/hrs. (2) material: percent ondry weight As indicated in Table II, nitrocellulose treated with thealkylated diphenyl amines of the present invention (B1 and B4) showunexpected improvement in moisture resistance characteristics.

(E) Firing testing/ energy output/reliability Nitrocellulose pelletsproduced according to paragraph C above are subjected to the moistureconditions set forth in paragraph D above for a period of 2 hours.

The pellets are then used in a Model AP300 tool to fire 1.0 inch x inchdiameter drive pins into a Type 300 cast aluminum plate 1.0 inch inthickness.

The relative energy output of the pellets then may be assessed based onthe depth to which the fasteners are driven into the plate. The depth isaverage depth on number of actual firings out of five attempts.

The reliability of the firing may be assessed in the number orpercentage of firings v. misfirings had, in this case five attempts areused.

In the case of B5 there is slow burning in four out of five attempts.However, the slow burning does not amount to firing suflicient to drivethe fasteners to the exte nt that they make any penetration into thetest plate.

When dry control pellets based on formula B3 are tested they fire 5/5and their average penetration into the test plate is 18.0 mm.

The results of Table III indicate that the nitrocellulose chargesproduced in accordance with the present invention (Bl-B4) exhibitimproved moisture resistance, while nonetheless retaining good firingcharacteristics, both from the standpoint of energy output and firingpercentage.

As indicated previously, the moisture resistance of nitrocellulosecharges produced with the use of the sponsored alkylated diphenylamines, may be further improved by subjecting the charges to a laterheat treatment.

(P) Heat treatment of nitrocellulose charges TABLE IV Moisture pickuppercent on dry weight Nitrocellulose pellet material 4 hours 8 hours 24hours B1 (not heat treated) 2. 77 3. 58 4. 59 B1 (heat treated) 2.49 2.92 3. 79

The results set forth in Table IV indicate a definite advantage inmoisture resistance is obtained from the heat treatment.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in carrying out the above coating orimpregnating method and in the nitrocellulose explosive charges setforth without departing from the scope of the inven tion, it is intendedthat all matter contained in the above description shall be interpretedas illustrative and not in a limiting sense.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent of the United States is:

1. An explosive charge exhibiting improved moisture resistancecomprising a mass of particulate nitrocellulose coated with an alkylsubstitute diphenyl amine having the formula wherein the R is hydrogenor alkyl radical and R is an alkyl radical and the combination of R andR contains a total of 8 to 40 carbon atoms, the amine comprising 0.1 to5.0 weight percent on weight of the nitrocellulose.

2. An explosive charge according to claim 1 wherein the combination of Rand R contains a total of 10 to 20 carbon atoms.

3. An explosive charge according to claim 1 wherein the nitrocelluloseis in compacted form.

4. An explosive charge according to claim 1 wherein the alkylsubstituted diphenyl amine is dioctyl diphenyl amine.

5. A method for providing an explosive charge having improved moistureresistance, which comprises the steps of providing a suspension ofnitrocellulose in particulate form in water, adding to the suspension asolution of alkyl substituted diphenyl amine having the formula:

wherein R is hydrogen or alkyl radical, R is an alkyl radical and thecombination of R and R contains a total of 8 to 40 carbon atoms inorganic solvent to coat the nitrocellulose with the said amine andthereafter separating coated nitrocellulose from the water.

6. A method according to claim wherein the coated nitrocellulose afterseparation from the water is heated above about the melting point of theamine.

7. A method according to claim 5 wherein the suspension contains about 2to 20 weight percent of nitrocellulose.

References Cited UNITED STATES PATENTS 1,329,211 1/1920 Snelling et al.14911 1,329,212 1/1920 Snelling et al. 149-11X 2,033,217 3/1936Woodbridge 149-11 2,123,517 7/1938 Woodbridge 14911 2,125,941 8/1938Matter 149--11X 3,303,073 2/1967 Graham et a1. 14911X 3,138,496 6/1964Monical 149-11 CARL D. QUARFORTH, Primary Examiner S. J. LECHERT, 1a.,Assistant Examiner US. Cl. X.R. 14994,

